The present invention relates to a machining apparatus having a main spindle supported by magnetic bearings, and more particularly to a machining apparatus which carries out works with a tool attached to one end of the spindle which is supported by magnetic bearings.
In a conventional machining apparatus, the machining condition is generally fixed by the material of a work piece, the tool being used, the machining method, etc. Therefore machining under an optimum condition is difficult because it is difficult to follow changes of the loads which are caused by various factors including the change of cutting resistance resulting from the change in the sharpness of the tool. Because of this problem, it is difficult to improve the machining accuracy and machining efficiency.
Some of the machining apparatus have overcome the abovementioned problem. For example, one machining apparatus is capable of controlling machining by the use of changes of electric power supplied to a spindle driving motor. Another machining apparatus is capable of controlling machining by the use of changes of the bearing pressure during machining.
However, these conventional machining apparatus suffer from problems, such as, outputs from the detectors change due to changes in revolution of the spindle, friction torque of the bearing, temperature of the bearing, etc., and therefore the detection sensitivity is low, and the response speed is slow.